Represents the expected annualized forfeiture rate for options granted.

No definition available.

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- Definition

Represents the number of shares awarded for each restricted share units.

+ References

No definition available.

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- References

No definition available.

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- Definition

Unrecognized cost of unvested share-based compensation awards.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (i)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

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- Definition

Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(1)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(i)-(ii)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(2)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

Percentage of vesting of share-based compensation awards.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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Stock compensation - RSU and PSU Narrative (Details) - USD ($) $ in Millions	1 Months Ended		3 Months Ended	6 Months Ended
	Jul. 31, 2016	Jan. 31, 2014	Mar. 31, 2018	Jun. 30, 2016	Dec. 31, 2017
Stock Compensation Plans
Assumed annualized forfeiture rate (as a percent)			5.00%
Stock Options
Stock Compensation Plans
Vesting period	4 years			3 years
Unrecognized compensation
Unrecognized compensation cost for nonvested option (in dollars)			$ 118.1
Vesting period of recognition of the unrecognized compensation cost of nonvested awards			1 year 8 months 12 days
Restricted Stock Units (RSUs)
Stock Compensation Plans
Number of shares awarded for each RSU (in shares)		1
Percentage of units vesting at the end of each calendar year (as a percent)	25.00%
Vesting period	4 years			3 years
Granted (in shares)			92,290
Outstanding (in shares)			704,894		769,202
Unrecognized compensation
Unrecognized compensation cost for nonvested option (in dollars)			$ 52.2
Vesting period of recognition of the unrecognized compensation cost of nonvested awards			1 year 4 months 24 days
Restricted Stock Units (RSUs) \| President And Chief Executive Officer
Stock Compensation Plans
Percentage of units vesting at the end of each calendar year (as a percent)			16.70%
Granted (in shares)		400,000
Vested (in shares)			266,667
Outstanding (in shares)			133,333